Zirconium (Zr)

Stable isotopes of zirconium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Zr-90  40  50  89.904702 51.45%  96.80% Metal
Zr-90 40 50 89.904702 51.45% >98.00% Oxide
Zr-91  40  51  90.905643 11.22%  >88.00% Metal
Zr-91 40 51 90.905643 11.22% >88.00% Oxide
Zr-92 40 52 91.905038 17.15% >91.00% Oxide
Zr-94 40 54 93.906314 17.38% >98.00% Metal
Zr-94 40 54 93.906314 17.38% >98.00% Oxide
Zr-96 40 56 95.908275 2.80% >86.00% Oxide
Zr-96 40 56 95.908275 2.80% >86.00% Metal

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Zirconium was discovered in 1789 by Martin Heinrich Klaproth. Its name originates with the Arabic word zargun, meaning “gold color.”

Zirconium may exist as a hard, lustrous, silvery-gray, crystalline scale or as a bluish-black amorphous powder. It is corrosion-resistant. It starts as a close-packed hexagonal lattice and transforms to a body-centered cubic structure at 865 ºC. It is soluble in hot, very concentrated acids and aqua regia and is insoluble in water and cold acids. It exhibits quadrivalency in most of its compounds, although divalent and trivalent compounds also exist.

Solid metal zirconium is stable in air at ordinary temperatures, but it reacts slowly at 200 ºC. The reaction is more rapid at high temperatures. Reactions with hydrogen occur at temperatures of 300-1000 ºC, forming ZrH2, a brittle dihydride. Zirconium combines with halogens at high temperatures, forming tetrahalides. Reactions occur in the range of 200-400 ºC. Solid tetrahalides sublime above 300 ºC. Although stable to most acids, the metal is attacked by concentrated hydrochloric and sulfuric acids under boiling conditions or in the presence of aqua regia or hydrofluoric acid. The metal is stable in organic acids under all conditions.

The most important applications of zirconium involve its alloy, Zircaloy, which offers excellent mechanical and heat-transfer properties and great resistance to corrosion and chemical attack. Other uses are as an ingredient of explosive mixtures; as a “getter” in vacuum tubes; in making flash bulb, flash powder and lamp filaments; in rayon spinnerets; and in surgical appliances.

A suspected carcinogen, zirconium is not permitted in cosmetics (per the United States Food and Drug Administration). It is flammable and explosive in the form of dust, powder, borings or shavings.

Properties of Zirconium

Name Zirconium 
Symbol Zr 
Atomic number 40 
Atomic weight 91.224 
Standard state Solid at 298 °K
CAS Registry ID 7440-67-7 
Group in periodic table
Group name None 
Period in periodic table
Block in periodic table d-block 
Color Silvery white 
Classification Metallic 
Melting point 1852 °C
Boiling point 4377 °C
Vaporization point 4377 ºC
Thermal conductivity 22.7 W/(m·K) at 298.2 °K
Electrical resistivity 40.0 µΩ·cm at 20 °C 
Electronegativity 1.4 
Specific heat 0.27 kJ/kg K 
Heat of vaporization 580 kJ·mol-1
Heat of fusion 21 kJ·mol-1
Density of liquid 5.8 g/cm3 at 1852 °C
Density of solid 6.51 g/cm3 
Electron configuration  [Kr]4d25s2 
Atomic radius 1.60 Å 
Ionic radius Zr4+ in crystal: 0.84 Å (coordination number 8)
Oxidation states  +2, +3, +4 

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